In recent years, attention has been paid to wireless power supply, which does not use a power supply cord and a power transmission cable, as a power supply system that supplies power to a battery mounted on a hybrid automobile or an electric automobile. As one of techniques of the wireless power supply, a technique of resonance type is known (Patent Literatures 1 and 2).
The power supply system of resonance type includes a resonance circuit on a power supply side and a resonance circuit on a power receipt side disposed to be separated from each other. Each of the resonance circuit on the power supply side and the resonance circuit on the power receipt side includes a resonance coil and a capacitor connected to the resonance coil. Two kinds of resonance circuit are known, i.e., a series resonance circuit including a resonance coil and a capacitor connected in series and a parallel resonance circuit including a resonance coil and a capacitor connected in parallel.
A resonance frequency f of the resonance circuit on the power supply side and the resonance circuit on the power receipt side is represented by the following Equation (1), where L is inductance of the resonance coil, and C is capacitance of the capacitor.f=1/(2π sqrt(LC))   (1)
Non-contact power transmission from the power supply side to the power receipt side is implemented by causing the resonance circuit on the power supply side and the resonance circuit on the power receipt side to resonate.